k (glass) 1.4 W/m-K, from Table A.3 k (air) = 0.0239 W/m-K, from Table A.4, property evaluated @ 270 K 1. A 0.75-mx 1.5-m window is constructed of 6-mm-thick glass. On a cold night, the inside and outside surface temperatures of the glass are 16C and -24C, respectively. (a) What is the rate of heat loss through the glass? (b) The window is replaced by a double-paned window, in which two panes of glass are separated by an air space. If the spacing of the panes is 13 mm and the glass surface temperatures in contact with the interior air space are 12C and -18C, what is the new rate of heat loss from the window? (Hint: since the temperatures on the inside glass surfaces are given, you need only analyze conduction across the air gap.) 2. The convection heat transfer coefficient can have a great effect on how a person experiences temperature. Determine the convection heat flux from a person's hand in each of the circumstances below. In each case, the person's hand can be assumed to have a surface temperature of 30C. (a) Hand outside the window of a car moving at 20 mph in air at -15C with a convection coefficient of 40 W/m-K. (b) Hand in a slow moving stream of water at 10C with a convection coefficient of 900 W/m-K. (c) Hand in still air in an air conditioned room at 20C with a convection coefficient of 3 W/m-K.